French Patent No. - FR-2 135 983 describes a torque converter for an automobile vehicle which enables the engine torque to be distributed differently to the front and rear axles when a difference in speed occurs between the front and rear wheels. This converter comprises a hydraulic coupling which produces a torque starting from a predetermined difference in speed, this torque causing the axial displacement of a ring which in its turn acts on the pressure plate of a multi-disc clutch mounted between the two shafts.
However, the hydraulic coupling must itself provide the clutch control and must be able to transmit relatively large torques.
Another disadvantage is that the control of the multi-disc clutch is realized by means of rollers which are displaced on ramps to cause displacement of the ring which acts on the pressure plate of the clutch. Such a structure is complex by nature and imposes the need for exact machining of the ramps to avoid any possible jamming of the rollers.
The object of the invention is to overcome these disadvantages and in a general manner proposes for this purpose a system which substitutes for a mechanical control, a hydraulic control of the coupling clutch responsive to a difference in speed between the two shafts.